Lithium-sulfur (Li/S) batteries have a theoretical capacity nearly one magnitude higher than that of LiFePO4. Nevertheless, the Li/S system has not yet been implemented in many applications because the following problems still need to be solved before sulfur cathode materials can be practically used in rechargeable lithium batteries: 1) particle size of sulfur should be made as fine as possible to ensure a high utilization rate of sulfur and then a high reversible capacity upon cycling; 2) discharge products of poly-sulfides should be carefully restrained from dissolving into electrolyte to ensure long cycle life; and 3) conductivity of the cathode material should be enhanced to ensure a better rate performance.
It is well-known that carbon nanotubes (CNTs) show excellent electric conductivity, however, their relatively smooth surface makes it difficult to load sulfur. On the other hand, a sulfur-carbon composite always suffers from the problem of dissolution of polysulfides into the electrolyte, which may cause capacity fade during cycling.